This patent application claims priority based on a Japanese patent applications, H11-156274 filed on Jun. 3, 1999, H11-184851 filed on Jun. 30, 1999, and H11-199110 filed on Jul. 13, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a glass base material, which is a parent material of an optical fiber.
2. Description of the Related Art
A raw material of an optical fiber is manufactured by hydrolyzing a raw material such as SiCl4 or GeCl4 by oxyhydrogen flame or hydrogen flame. The hydrolyzed raw material is accumulated on a starting material or grown from a seed crystal to form a porous glass base material. There are various methods for manufacturing a porous glass base such as an outside vapor deposition method (OVD method) and a vapor-phase axial deposition method (VAD method). The porous glass base material is dehydrated and sintered, to form a glass base material having a large diameter. A glass fiber preform is formed by reducing the diameter of the glass base material, which has large diameter. The glass fiber preform is drawn, thus producing a glass fiber.
The raw material such as SiCl4 or GeCl4 is vaporized in a vaporizing unit for supply to a hydrolyzing process. A vaporizing unit vaporizes the raw material by heating the raw material under atmospheric pressure. If the vaporizing unit is continuously used, the raw material is kept at a high temperature for a long period which induces autolysis. This is partial hydrolyzation caused by the small amount of water existing as a foreign impurity, gelation, and crystallization of foreign impurities. Therefore, the purity of the raw material decreases, and thus the quality of the glass base material also decreases.
An apparatus called a bubbler is also used as the vaporizing unit. The bubbler heats the raw material to a lower temperature under a decompressed condition, and bubbles a carrier gas such as oxygen or argon through the raw material. The bubbler may cause a clog in a supplying pipe which supplies the raw material for the hydrolyzing process, or a valve, which is provided on the supplying pipe, after a long period of continuous use. The clog may cause fluctuation of an equilibrium vapor pressure so that the partial pressure of the raw material among a mixture of the raw material in gas phase and a carrier gas, fluctuates. If the partial pressure of the raw material fluctuates, the hydrolyzed raw material cannot be accumulated homogeneously. Therefore, the quality of the glass base material is not uniform and stable.
The constituent components of the apparatus for manufacturing the porous glass base material must be exchanged if the constituent components are clogging due to the gel material and foreign impurities contained in the material gas. When the constituent components are exchanged, the material gas may contact with water contained in open air, thus causing formation of another gel material and corrosive gas that can cause a new clog. Therefore, air in the exchanged component must be completely removed and replaced with the gas raw material and the carrier gas each time following exchange of the constituent components. It takes time and labor to exchange the constituent components, so that the productivity for manufacturing the glass base material decreases.
Therefore, it is an object of the present invention to provide an apparatus for manufacturing a glass base material and method for manufacturing glass base material which overcome the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present embodiment, an apparatus for manufacturing a glass base material which is a parent material of an optical fiber, comprises: a tank which contains a raw material of the glass base material, within which vaporization of the raw material occurs, to generate a raw material in gas phase; a temperature control unit which controls a temperature of the raw material; and a pressure control unit which controls pressure of the raw material in gas phase.
The apparatus can be provided such that the tank may include a gas phase region, which contains the raw material in gas phase; and a liquid phase region, which contains the raw material in liquid phase. The temperature control unit and the pressure control unit may control the partial pressure of the raw material in gas phase in the gas phase region by controlling an equilibrium vapor pressure in the gas phase region and the liquid phase region. The pressure control unit may have a carrier gas supply unit, which supplies a carrier gas for controlling the equilibrium vapor pressure by bubbling the carrier gas through the liquid phase region. The carrier gas supply unit may have a carrier gas cylinder, which supplies the carrier gas to the carrier gas supply unit.
The apparatus may further comprise at least one reaction vessel where the raw material in gas phase is supplied and the glass base material is formed by hydrolyzing the raw material in gas-phase. The apparatus may additionally comprise a gas material supply valve that controls the flow rate of the raw material in gas phase from the tank to the reaction vessel, and a filter which filters the raw material in gas phase supplied to the reaction vessel. The filter may be formed by a membrane that has a transmitting hole for filtering the raw material in gas phase. A diameter of the transmitting hole may be substantially from 0.1 xcexcm to 100 xcexcm. The membrane may be made of a politetrafluoroethylene, a stainless sinter, a stainless fiber, or a ceramic filter. The filter may have a plurality of layers of membranes.
The reaction vessel may have a cooling unit which cools the reaction vessel, and the cooling unit may circulate cooling water which contains anticorrosive chemicals inside the cooling unit. The anticorrosive chemicals may include policarboxylic acid nitrite. The cooling water may contain the policarboxylic acid nitrite at a concentration from 1 ppm to 10 ppm. The anticorrosive chemicals may further include inorganic nitride. The cooling water may contain each of the policarboxylic acid nitrite and inorganic nitride at concentrations from 1 ppm to 10 ppm. Temperature of the cooling water may be substantially from 40xc2x0 C. to 90xc2x0 C., preferably substantially from 50xc2x0 C. to 80xc2x0 C. The cooling water may contain an antiblastic agent that suppresses an increase of bacteria.
According to second aspect of the present embodiment, a method for manufacturing a glass base material can be provided such that the method comprises: providing a raw material of the glass base material, heating the raw material to vaporize the raw material and generate a raw material in gas phase, supplying a carrier gas to reduce a partial pressure of the raw material in gas phase to vaporize the raw material, controlling a temperature of the raw material by adjusting the heating of the raw material, and controlling the partial pressure of the raw material in gas phase by adjusting the supply of the carrier gas. The method may further comprise, supplying and hydrolyzing the raw material in gas phase to form the glass base material.
The method may further comprise, filtering the raw material in gas phase and supplying and hydrolyzing the filtered raw material in gas phase. The method may further comprise, controlling a flow rate of the raw material in gas phase and supplying and hydrolyzing the flow rate controlled raw material in gas phase. Supplying and hydrolyzing the raw material in gas phase may hydrolyze the raw material in gas phase, in a reaction vessel; and the hydrolyzing may include cooling the reaction vessel by circulating cooling water around the reaction vessel. The cooling may cool the reaction vessel with cooling water that contains anticorrosive chemicals. The anticorrosive chemicals may include policarboxylic acid nitrite. The cooling water may contain policarboxylic acid nitrite at a concentration substantially from 1 ppm to 10 ppm. The anticorrosive chemicals may further include inorganic nitride. The cooling water may contain inorganic nitride at a concentration substantially from 1 ppm to 10 ppm. The cooling may regulate a temperature of the cooling water substantially from 40xc2x0 C. to 90xc2x0 C., preferably from 50xc2x0 C. to 80xc2x0 C. The cooling water may contain an antiblastic agent that suppresses an increase of bacteria in the cooling water.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.